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We report on a VLA survey for late-time radio emission from 59 supernovae(SNe) of Type I b/c, which have been associated with long-duration gamma-raybursts (GRBs). An "off-axis" GRB burst (i.e. whose relativistic jet points awayfrom us) is expected to have late-time radio emission even in the absence ofsignificant prompt gamma-ray emission. From our sample, we detected only SN2003gk with an 8.4-GHz flux density of $2260 \pm 130 \,\mu$Jy. Our subsequentVLBI observations of SN 2003gk, at an age of $\sim$8 yr, allowed us todetermine its radius to be $(2.4 \pm 0.4) \times 10^{17}$ cm, or $94 \pm 15$light days. This radius rules out relativistic expansion as expected for anoff-axis GRB jet, and instead suggests an expansion speed of $\sim 10\:000$ kms$^{-1}$ typical for non-relativistic core-collapse supernovae. We attributethe late-onset radio emission to interaction of the ejecta with a dense shellcaused by episodic mass-loss from the progenitor.  In addition, we present new calculations for the expected radio lightcurvesfrom GRB jets at various angles to the line of sight, and compare these to ourobserved limits on the flux densities of the remainder of our SN sample. Fromthis comparison we can say that only a fraction of broadlined Type I b/c SNehave a radio-bright jet similar to those seen for GRB afterglows atcosmological distances. However, we also find that for a reasonable range ofparameters, as might be representative of the actual population of GRB eventsrather than the detected bright ones, the radio emission from the GRB jets canbe quite faint, and that at present, radio observations do not place strongconstraints on off-axis GRB jets.

Radio limits on off-axis GRB afterglows and VLBI observations of SN 2003gk